Polyester composition with enhanced gas barrier, articles made therewith, and methods

ABSTRACT

A polyester composition with enhanced gas barrier properties comprises a polyester and an organic gas barrier enhancing additive having the chemical formula OH-AR—OH, wherein AR is substituted or unsubstituted naphthalene. Articles with enhanced gas barrier and methods for making gas barrier enhanced polyesters and articles are disclosed.

CROSS-REFERENCE

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application 60/558,494 filed on Apr. 1, 2004, the disclosureof which is expressly incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to polyester and polyester articles. Inparticular, this invention relates to polyesters for use in applicationssuch as packaged beverages wherein enhanced gas barrier or oxygenscavenging is desirable.

BACKGROUND OF THE INVENTION

Polyethylene terephthalate and its copolyesters (hereinafter referred tocollectively as “PET”) are widely used to make containers for carbonatedsoft drinks, juice, water, and the like due to their excellentcombination of clarity, mechanical, and gas barrier properties. In spiteof these desirable characteristics, insufficient gas barrier of PET tooxygen and carbon dioxide limits application of PET for smaller sizedpackages, as well as for packaging oxygen sensitive products, such asfood, beer, juice, and tea products. A widely expressed need exists inthe packaging industry to further improve the gas barrier properties ofPET.

The relatively high permeability of PET to carbon dioxide limits the useof smaller PET containers for packaging carbonated soft drinks. Thepermeation rate of carbon dioxide through PET containers is in the rangeof 3 to 14 cc's per day or 1.5 to 2% per week loss rate at roomtemperature depending on the size of the container. A smaller containerhas a larger surface to volume ratio resulting in a higher relative lossrate. For this reason, PET containers are currently used only as largercontainers for packaging carbonated soft drinks, while metal cans andglass containers are the choice for smaller carbonated soft drinkcontainers.

Numerous technologies have been developed or are being developed toenhance the barrier of PET to small gas molecules. For example, externalor internal coatings for enhancing the gas barrier of PET containershave been developed. The coating layer is normally a very high barrierlayer, either inorganic or organic, and slows down the diffusion ofgases. Implementation of this technology, however, requires coatingequipment not normally utilized in the manufacture of packaged beveragesand therefore requires substantial capital investment, increased energyusage, and increased floor space. In many beverage packaging plants thatare already crowded, the additional space is not an option.

Multi-layered containers have also been developed with a high barrierlayer sandwiched between two or more PET layers. Implementation of thistechnology also requires substantial capital investment and delaminationof the container layers impacts appearance, barrier, and mechanicalperformance of the containers.

A barrier additive for the PET or a polymer with inherent barrierproperties would be preferred solutions. Neither such solution requiresadditional capital investment, and therefore, does not have thelimitations inherent with other technologies. A barrier additive canalso be added during the injection molding process which gives moreflexibility for downstream operations.

L. M. Robeson and J. A. Faucher disclose in J. Polymer Science, Part B7, 35-40 (1969) that certain additives could be incorporated intopolymers to increase their modulus and gas barrier properties through anantiplasticization mechanism. This article discloses utilizing additiveswith polycarbonate, polyvinyl chloride, polyphenylene oxide, andpolythyelene oxide.

In WO 01/12521, Plotzker et al. proposed the use of additives selectedfrom 4-hydroxybenzoates and related molecules to increase the gasbarrier properties of PET. This published patent application disclosesbarrier additives of the following structure:HO—Ar—COOR, HO—Ar—COOR1COO-AR—OH, HO-AR—CONHR, HO-AR—CO—NHR3-COO-AR—OH,HO-AR—CONHR2NHCO-AR—OH

In the foregoing structure, AR is selected from the group consisting ofsubstituted or unsubstituted phenylene or naphthalene. And R1, R2, andR3 are selected from the group consisting from C1 to C6 alkyl groups, aphenyl group, and a naphthyl group.

The foregoing additives described in the art provide only moderateimprovement in PET barrier, less than 2.1 times (×) for oxygen barrierfor the best examples with a 5 weight percent loading level. At thisloading level, however, PET experiences substantial degradation and asignificant drop in intrinsic viscosity (IV). Although lowering thelevel of additive reduces the degradation of PET, it also reduces thebarrier improvement factor, so much so that no real benefit exists inusing these additives in packaging carbonated soft drinks or oxygensensitive food. Furthermore, PET with a significantly lower IV cannot beused in blow molding containers, such as beverage containers.Furthermore, lower IV PET makes containers with poor mechanicalperformance, such as creep, drop impact, and the like. Still further,PET containers made from lower IV PET have poor stress crackingresistance, which is undesirable in container applications.

PET has been modified or blended with other components to enhance thegas barrier of the PET. Examples include polyethylene naphthalate(PEN)/PET copolymers or blends, isophthalate (IPA) modified PET, PETblended with polyethylene isophthalate (PEI) or a polyamide, such asnylon, and PET modified with resorcinol based diols. For a PET copolymerto achieve moderate barrier enhancement of 2× or higher, themodification is normally more than 10 to 20 weight or mole % of thetotal co-monomers. When PET is modified to such a high level, thestretching characteristics of the PET are changed dramatically such thatthe normal PET container preform design could not be used in themanufacture of containers. Using these PET copolymers to moldconventional PET container preforms results in preforms that can not befully stretched and the ultimate containers are very difficult, if notimpossible, to make. Even if such a container can be made, it does notshow improved barrier performance and shows deteriorated physicalperformance such that it can not be used to package carbonated softdrinks. U.S. Pat. Nos. 5,888,598 and 6,150,450 disclose redesigned PETcontainer preforms with thicker side walls to compensate for theincreased stretch ratio. This thicker preform, however, requires newmolds which require additional capital investment and is also made at alower rate of productivity because it takes longer to cool and heat thethicker wall preform. Furthermore, PET blends with polyamide such asnylon developed yellowness and haze and are not clear like conventionalPET.

Products sensitive to oxygen, such as foods, beverages and medicines,deteriorate and spoil in the presence of oxygen. To prevent oxygeningress to the products, different oxygen scavenger technologies havebeen developed. These oxygen scavengers are called active barriertechnologies. They are different from the passive barrier technologiesthat work to improve barrier to small gas molecules only. U.S. Pat. No.5,021,515 discloses a multi-layered, nylon based oxygen scavenger. U.S.Pat. No. 5,744,056 discloses an oxygen scavenger composition that can beincorporated into bottle sidewall in a monolayer fashion. Similarly,U.S. Pat. No. 5,700,554 discloses an oxygen scavenger composition. Themonolayer oxygen scavengers provide additional benefits over themulti-layered oxygen scavenger in that the monolayer oxygen scavengercan react with the headspace oxygen in the container, in addition toblocking the oxygen ingress to the container. Therefore, the monolayeroxygen scavenger can prevent the product oxidation from the headspaceoxygen. The oxygen scavenger compositions disclosed in these and othersimilar patents, however, all contain transition metals as catalysts.The transition metals can cause degradation in PET and causediscoloration in PET. In addition, in certain countries, certaintransition metals also raise environmental and regulatory concerns.

Thus, there is a need in the art to enhance the barrier performance ofPET for use in applications that will require enhanced barrier, such asin the packaging of carbonated beverages and oxygen sensitive beveragesand foods, in a manner that does not cause substantial degradation ofthe PET, does not substantially impact the stretch ratio of the PET,does not include transition metals, and allows the use of existing PETperform toolings.

SUMMARY OF THE INVENTION

This invention addresses the above described need for enhanced gasbarrier PET by providing a polyester composition comprising a polyesterand an organic gas barrier enhancing additive having the chemicalformula OH-AR—OH, wherein AR is substituted or unsubstitutednaphthalene.

In accordance to a particular embodiment, the polyester in the polyestercomposition comprises a poly(ethylene terethphalate) based copolymer(PET copolymer). In a desired embodiment, the polyester comprises a PETcopolymer having less than 20% diacid component modification and/or lessthan 10% diol component modification, based on 100 mole % diacidcomponent and 100 mole % diol component. With the organic gas barrierenhancing additive, this embodiment provides acceptable gas barrierdespite having a low level of diacid or diol modification, if anymodification. Without wishing to be bound by theory, it is believed thatsome embodiments of this invention possess gas barrier capability, whileanother possesses more oxygen scavenging capability or both gas barrierand oxygen scavenging capability.

According to another embodiment, this invention encompasses a method forenhancing gas barrier of a polyester composition comprising blending apolyester and an organic gas barrier enhancing additive having thechemical formula OH-AR—OH, wherein AR is substituted or unsubstitutednaphthalene. According to a preferred embodiment, the polyester is a PETcopolymer.

According to still another embodiment, this invention encompasses anarticle comprising a polyester and an organic gas barrier enhancingadditive having the chemical formula OH-AR—OH, wherein AR is substitutedor unsubstituted naphthalene. According to a particular embodiment, thearticle is a container and in other preferred embodiments is a stretchblow molded container. In a preferred embodiment, the polyester is a PETcopolymer.

According to yet another embodiment, this invention encompasses a methodfor making an article with enhancing gas barrier comprising the steps ofblending a polyester and an organic gas barrier enhancing additivehaving the chemical formula OH-AR—OH, wherein AR is substituted orunsubstituted naphthalene. In a particular embodiment, the polyester isa PET copolymer. Furthermore, in another embodiment, the article is astretch blow molded container.

Particular embodiments of this invention provide polyesters, such as PETcopolymers, with enhanced gas barrier, and in particular, enhancedbarrier to carbon dioxide and oxygen. This makes certain embodiments ofthis invention particularly suited for packaging carbonated soft drinksand oxygen sensitive beverages and foods. Particular embodiments achievethis enhanced gas barrier while maintaining acceptable physicalproperties.

Other objects, features, and advantages of this invention will becomeapparent from the following detailed description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of a system for making a PETcontainer with enhanced gas barrier in accordance with an embodiment ofthis invention.

FIG. 2 is a sectional elevation view of a molded container preform madein accordance with an embodiment of this invention.

FIG. 3 is a sectional elevation view of a blow molded container madefrom the preform of FIG. 2 in accordance with an embodiment of thisinvention.

FIG. 4 is a perspective view of a packaged beverage made in accordancewith an embodiment of this invention.

DETAILED DESCRIPTION OF EMBODIMENTS

This invention encompasses a polyester composition with enhanced gasbarrier or oxygen scavenging capability or both, a method for enhancinggas barrier or oxygen scavenging capability of a polyester composition,articles comprising such a polyester composition, and a method formaking such articles. As explained in more detail below, embodiments ofthis invention provide a polyester composition and articles madetherewith which exhibit enhanced barrier to gases or oxygen scavengingcapability while maintaining physical properties.

This invention is applicable to any polyester and is suitable for usesin which a high gas barrier is desirable. Suitable polyesters includethose that are suitable for packaging carbonated or non-carbonatedbeverages and oxygen sensitive beverages or food products. Suitablepolyesters for use in embodiments of this invention include PETcopolymers, polyethylene naphthalate (PEN), polyethylene isophthalate,and the like. PET copolymers are particularly useful because they areused for many barrier applications such as films and containers.Suitable containers include but are not limited to bottles, drums,carafes, coolers, and the like.

PET copolymers suitable for use in embodiments of this inventioncomprise a diol component having repeat units from ethylene glycol and adiacid component having repeat units from terephthalic acid. Desirably,in some embodiments, the PET copolymer has less than 20% diacidcomponent modification and/or less than 10% diol component modification,based on 100 mole % diacid component and 100 mole % diol component. SuchPET copolymers are well known.

In accordance with embodiments of this invention, suitable organic gasbarrier enhancing additives are those having the chemical formulaOH-AR—OH, wherein AR is substituted or unsubstituted naphthalene.Suitable additives include, but are not limited to, 1,2-dihydroxynaphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxy naphthalene,1,6-dihydroxy naphthalene, and 2,6-dihydroxy naphthalene. 1,5-dihydroxynaphthalene degrades at polyester melt processing temperatures, andtherefore is not a preferred additive, but is useful at lower meltprocessing temperatures. 2,7-dihydroxy naphthalene is not listed becauseit has an even lower degradation temperature and is not suitable for useas an additive for PET.

The organic gas barrier enhancing additive compound is added to thepolyester in an amount sufficient to enhance the gas barrier propertiesof the polyester. In accordance with an embodiment of this invention,the polyester is present in the polyester composition in amount from99.9% to 90% by weight of the polyester composition and the organic gasbarrier enhancing additive is present in the polyester composition in anamount of 0.1% to about 10% by weight of the polyester composition. Inaccordance to another embodiment of this invention, the PET copolymer ispresent in the polyester composition in an amount from 99.9% to about95% by weight of the polyester composition and the additive is presentin the polyester composition in an amount from about 0.1% to about 5% byweight of the polyester composition. In accordance with still anotherembodiment of this invention, the PET copolymer is present in thepolyester composition in an amount from about 99.9% to about 97% byweight of the polyester composition and the additive is present in thepolyester composition in an amount from about 0.1% to about 3% by weightof the polyester composition.

Polyesters, including PET copolymers, have free volume between polymerchains. As is known to those skilled in the art, the amount of freevolume in polyesters such as PET copolymers determines their barrier togas molecules. The lower the free volume, the lower the gas diffusion,and the higher the barrier to gas molecules. In some embodiments, it isbelieved that the additive is at least partially disposed in the freevolume of the polyester between the polyester chains and solidifies inthe free volume when the blend is cooled down to room temperature aftermelt processing. Due to the presence of the two hydroxyl groups, it ispossible that the additive reacts with the polyester chain and causesthe intrinsic viscosity (IV) to drop although the reactivity of thehydroxy group in the current additive is very low. Therefore, when meltblending the additive with polyester, it is possible that the additivepartially reacts with the polyester and forms a mixture ofpolyester/dihydroxy naphthalene copolymer, polyester, and the additive.For example, when the additive is 1,3-dihydroxy naphthalene, it isbelieved that the additive at least partially reacts with the polyesterand becomes part of the polyester backbone chain. According to aparticular embodiment, the polyester comprises a poly(ethyleneterephthalate) based copolymer (PET copolymer) and, based on 100 mole %diacid component and 100 mole % diol component, the PET copolymer hasless than 20% diacid component modification and less than 10% diolcomponent modification, and at least a portion of the additive isreacted with the PET copolymer such that the diol component comprises0.1 to about 5 mole % of the additive.

The additive may be incorporated into the polyester in different ways.For example, at lower loading levels, i.e., 3 weight % or below, theadditive can be incorporated directly into polyester during theinjection molding process, can be preblended in the polyester resinmaking process, or can be incorporated into melt polyester prior to thedischarge of the polyester in the melt polymerization process. At higherloading levels, 3 weight % or higher, the additives can be preblendedwith the polyester, melt extruded and solid state polymerized to thedesired IV. The solid stated mixture can then be injection molded intocontainer performs as described in more detail below.

In some embodiments, it is desirable to reduce the latent effect of anyresidual polycondensation catalyst in the polyester. These catalystsinclude commonly used catalyst such as compounds containing antimony,titanium, tin, and the like, and are deactivated by phosphoruscontaining compounds. The phosphorus containing compounds include bothorganic and inorganic compounds. Examples include but are not limited tophosphoric acid, polyphosphoric acid, and tris(2,4-di-t-butylphenyl)phosphite, tris monononylphenyl phosphite. These additives are typicallyadded in amounts less than 2000 ppm.

As described above, the polyester composition of this invention isuseful for making articles in which enhanced gas barrier is desirable.In short, such articles are made by forming the above describedpolyester compositions into the desired article by conventional methodssuch as melt forming. Suitable melt forming processes include, but arenot limited to, injection molding, extrusion, thermal forming andcompression molding.

In particular, embodiments of this invention are suitable for makingcontainers for packaging applications in the carbonated andnon-carbonated soft drink industry and the food industry. A commonmanufacturing method for forming these containers includes injectionmolding container preforms, and then, making the containers from thepreforms in single stage, two stage, and double blow moldingmanufacturing systems. Such methods are well known to those skilled inthe art and examples of suitable preform and container structures andare disclosed in U.S. Pat. No. 5,888,598, the disclosure of which isexpressly incorporated herein by reference in its entirety.

More particularly, a container preform is formed by injection moldingthe polyester into a blowable geometric form. The preform or blowableform is then contained within a mold cavity having the volumetricconfiguration of the desired container and the preform is expanded byblowing it with compressed air within the confines of the mold cavity.

Commercially available equipment, as is used in the manufacture of thinwalled single use PET beverage containers, may be used to make thecontainers in accordance with embodiments of the present invention. Inaddition, commercial equipment like that used in manufacturingconventional thick wall refillable PET containers may also be used.

Suitable containers in accordance with embodiments of this invention maybe blow-molded from a cylindrical injection-molded preform having anopen top end and neck finish. The preform may have a taperedshoulder-forming portion, substantially uniform thickness along thesides of the cylinder, and a base-forming portion preferably in achampagne design, but including a hemispherical base with a base cup ora footed design such as a petaloid design. In preferred embodiments, thepreform is amorphous and substantially transparent and is injectionmolded.

In accordance with preferred embodiments of this invention, containerpreforms are subsequently placed in a blow molding apparatus having anupper mold section which engages the neck finish, a middle mold sectionhaving an interior cavity forming the shape of the container side wall,and a lower mold section having an upper surface forming the outwardlyconcave dome portion of the container base. In accordance with astandard reheat stretch blow mold process, the injection-molded preformis first reheated to a temperature suitable for stretching andorientation of about 70 to 130° C., placed in the blow mold, and anaxial stretch rod is then inserted into the open upper end and moveddownwardly to axially stretch the preform. Subsequently orsimultaneously, an expansion gas is introduced into the interior of thepreform to radially expand the shoulder, sidewall and base formingportions outwardly into contact with the interior surfaces of moldsections. The resulting blown container has the same neck finish withouter threads and lowermost neck flange as the preform. The remainder ofthe bottle undergoes expansion, although to varying degrees. A removablecap is attached to the open upper end of the container. The cap includesa base portion having internal threads which engage the outer threads onthe neck finish.

FIG. 1 illustrates a system 10 in accordance with an embodiment of thisinvention for making a rigid container preform 12 (illustrated in FIG.2) and a rigid container 14 (illustrated in FIG. 3) from the preform. Asis shown in FIG. 1, solid PET copolymer pellets 20 and an organic gasbarrier enhancing additive such as dimethyl terephthalate 22 are addedto a feeder or hopper 24 that delivers the components to a hot meltextruder 26 in which the components are melted and blended. The hot meltextruder 26 then extrudes the molten mixture of PET copolymer andorganic gas barrier enhancing additive into an injection molding device28 to form the preform 12. The preform is cooled and removed from theinjection molding device 28 and delivered to a blow molding device 30which blow molds the preform 12 into a finished rigid container 14.

As explained above, the melt residence time of the preform production ispreferably less than three minutes and more preferably from about 100 toabout 120 seconds. The melt temperatures desirably from 270 to about300° C. and more desirably from about 270 to about 290° C. The meltresidence time begins when the PET copolymer and organic barrierenhancing additive enter the melt extruder 26 and start melting, andends after injection of the molten blend into the injection mold to formthe preform 12.

Turning to FIG. 2, a polyester container preform 12 is illustrated. Thispreform 12 is made by injection molding PET based resin and comprises athreaded neck finish 112 which terminates at its lower end in a cappingflange 114. Below the capping flange 114, there is a generallycylindrical section 116 which terminates in a section 118 of graduallyincreasing external diameter so as to provide for an increasing wallthickness. Below the section 118 there is an elongated body section 120.

The preform 12 illustrated in FIG. 2 can be blow molded to form acontainer 14 illustrated in FIGS. 3 and 4. The container 14 comprises ashell 124 comprising a threaded neck finish 126 defining a mouth 128, acapping flange 130 below the threaded neck finish, a tapered section 132extending from the capping flange, a body section 134 extending belowthe tapered section, and a base 136 at the bottom of the container. Thecontainer 14, for the most part, is highly biaxially oriented, but theneck finish 126 is non-oriented. The container 14 is suitably used tomake a packaged beverage 138, as illustrated in FIG. 4. The packagedbeverage 138 includes a beverage such as a carbonated soda beveragedisposed in the container 14 and a closure 140 sealing the mouth 128 ofthe container.

The preform 12, container 14, and packaged beverage 138 are but examplesof applications using the preforms of the present invention. It shouldbe understood that the process and apparatus of the present inventioncan be used to make preforms and containers having a variety ofconfigurations.

The present invention is described above and further illustrated belowby way examples which are not to be construed in any way as imposinglimitations upon the scope of the invention. On the contrary, it is tobe clearly understood that resort may be had to various otherembodiments, modifications, and equivalents thereof which, after readingthe description herein, may suggestion themselves to those skilled inthe art that without departing from the scope of the invention and theappended claims.

EXAMPLE 1

A commercially available polyester container grade resin was used as acontrol. The polyester composition (PET) had a diacid component of 97.2mole % terephthalic acid and 2.8 mole % isophthalic acid and a glycolcomponent of 97.2 to 97.3 mole % ethylene glycol and 2.7 to 2.8 mole %diethylene glycol. The PET was dried in a vacuum oven at 140° C.overnight to a moisture level below 50 ppm. The additives listed inTable 1 were dried in a vacuum oven at 70° C. overnight to removeabsorbed moisture. The PET and 5 weight % of different additives weremixed prior to injection molding. A lab scale Arburg unit cavityinjection molding machine was used for injection molding. A 24.5-gpreform was used to make a 500 ml container. The preforms were blowmolded with a Sidel SBO 2/3 blow molding machine to make acceptable 500ml contour containers. The oxygen transmission rate of the containerswas then measured using a Macon 2/60 model instrument at 22.2° C. and50% relative humidity (RH) with the 99% N₂/1% H₂ purging rate of 10ml/min on one side and air on the other side. The results are shown inTable 1. The barrier improvement factor (BIF) was defined as the ratioof the oxygen transmission rate of the control and the additive package.BIF is a measurement of the barrier enhancement as comparison tocontrol.

Table 1 Oxygen transmission rate of the control and additive containersat 5 weight % additive loading TABLE 1 O₂ transmission rate BarrierImprovement Additive (cc/pkg/day) Factor (BIF) PET Control 0.046 1.001,5 dihydroxy naphthalene 0.0097 4.74 1,6 dihydroxy naphthalene 0.0059.20 2,6 dihydroxy naphthalene 0.0064 7.19

EXAMPLE 2

The resins and additives listed in Table 2 were dried, mixed andinjection molded as in Example 1. Instead of 5 weight % of additiveloading, a 3 weight % of additive loading was used. A 24.5-g preform wasused to make a 500 ml container. The preforms were blow molded with aSidel SBO 2/3 blow molding machine to make acceptable 500 ml contourcontainers. The oxygen transmission rate of the containers was thenmeasured using a Macon 2/60 model instrument at 22.2° C. and 50% RH withthe 99% N₂/1% H₂ purging rate of 10 ml/min on one side and air on theother side. The results are shown in Table 2. TABLE 2 Oxygentransmission rate of the control and additive containers at 3 weight %additive loading O₂ transmission rate Barrier Improvement Additive(cc/pkg/day) Factor (BIF) PET control 0.046 1.0 1,6 dihydroxynaphthalene 0.008 5.75 2,6 dihydroxy naphthalene 0.008 5.75

EXAMPLE 3

A commercially available carbonated soft drink grade PET resin and 3weight % 1,3-dihydroxy naphthalene were dried, mixed and injectionmolded as in Example 1. A 24.5 g preform was used to make a 500 mlcontainer. The preforms were blow molded with a Sidel SBO 2/3 blowmolding machine to make acceptable 500 ml contour containers. The bottlesidewalls were then cut into a 2 in by 2 in square and mounted into aMocon Permeatran to measure the CO₂ transmission rate. A PET controlfilm was also used for the CO₂ transmission rate. The results are shownin table 3. TABLE 3 CO₂ transmission rate of the control and additivefilms CO₂ transmission rate Barrier Improvement Additive (cc/mil/100in²/day) Factor (BIF) PET control 29.1 1.0 3 weight % 1,3 13.7 2.12dihydroxy naphthalene

EXAMPLE 4

A commercially available carbonated soft drink grade PET resin and 5weight % of 1,3 dihydroxy naphthalene additive were dried, mixed andinjection molded as in Example 1. A 24.5-g preform was used to make a500 ml container. The preforms were blow molded with a Sidel SBO 2/3blow molding machine to make acceptable 500 ml contour containers. Theoxygen transmission rate of the containers were then measured using aMacon 2/60 model instrument at 22.2° C. and 50% RH with the 99% N₂/1% H₂purging rate of 10 ml/min on one side and air on the other side. Theresults are shown in Table 4. TABLE 4 Oxygen transmission rate of thecontrol and additive containers O₂ transmission Barrier ImprovementAdditive rate (cc/pkg/day) Factor (BIF) PET control 0.046 1.00 5 weight% 1,3 dihydroxy 0.0000 NA naphthalene

Surprisingly, the 5 weight % 1,3 dihydroxy naphthalene gave unexpectedlow oxygen transmission rate. The O₂ transmission rate was too low to bedetected from the measurement equipment. This clearly showed an oxygenscavenger effect. This oxygen scavenger composition has the addedbenefit over the prior art oxygen scavenger composition in that it doesnot contain any transition metals.

EXAMPLE 5 (COMPARISON EXAMPLES)

The resins and additives were dried, mixed and injection molded as inExample 1. Two comparison additives were used. One was selected from thebest performing additive list from WO 01/12521,methyl-4-hydroxy-benzonate. Another was selected from a high barriercomonomer from U.S. Pat. No. 6,320,014, 1,3-dihydroxy benzene. Theadditives were added at 3 weight % first, then at 5 weight %. When addedat 5 weight %, excessive degradation occurred for the 1,3-dihydroxybenzene. The excessive degradation caused substantial IV drop so much sothat acceptable containers could not be made. A 24.5-g preform was usedto make a 500 ml container. The preforms were blow molded with a SidelSBO 2/3 blow molding machine to make acceptable 500 ml contourcontainers. The oxygen transmission rate of the containers were thenmeasured using a Macon 2/60 model instrument at 22.2° C. and 50% RH withthe 99% N₂/1% H₂ purging rate of 10 ml/min on one side and air on theother side. The results are shown in Table 5. TABLE 5 Comparison oxygentransmission rate for the control and additive containers Barrier O₂transmission Improvement Additive Loading rate (cc/pkg/day) Factor (BIF)PET control 0.046 1.00 1,3 dihydroxy 3 wt % 0.034 1.35 benzeneMethyl-4-hydroxy 5 wt % 0.023 2.00 benzoate Methyl-4-hydroxy 3 wt % 0.031.53 benzoate

As can be seen from the data in table 5, embodiments of this inventionhave much higher gas barrier than containers made with conventionalbarrier additives.

It should be understood that the foregoing relates to particularembodiments of the present invention, and that numerous changes may bemade therein without departing from the scope of the invention asdefined by the following claims.

1. A polyester composition comprising: a polyester; and an organic gasbarrier enhancing additive having the chemical formula OH-AR—OH, whereinAR is substituted or unsubstituted naphthalene.
 2. A polyestercomposition as in claim 1 wherein the polyester is present in thepolyester composition in an amount from about 99.9% to about 90% byweight of the polyester composition and the additive is present in thepolyester composition in an amount from about 0.1% to about 10% byweight of the polyester composition.
 3. A polyester composition as inclaim 1 wherein the additive is selected from the group comprising1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxy naphthalene.4. A polyester composition as in claim 1 wherein the additive is1,3-dihydroxy naphthalene.
 5. A polyester composition as in claim 1wherein the polyester comprises a poly(ethylene terephthalate) basedcopolymer (PET copolymer) having less than 20% diacid componentmodification and/or less than 10% diol component modification, based on100 mole % diacid component and 100 mole % diol component.
 6. Apolyester composition as in claim 5 wherein the PET copolymer is presentin the polyester composition in an amount from about 99.9% to about 90%by weight of the polyester composition and the additive is present inthe polyester composition in an amount from about 0.1% to about 10% byweight of the polyester composition.
 7. A polyester composition as inclaim 5 wherein the PET copolymer is present in the polyestercomposition in an amount from about 99.9% to about 95% by weight of thepolyester composition and the additive is present in the polyestercomposition in an amount from about 0.1% to about 5% by weight of thepolyester composition.
 8. A polyester composition as in claim 5 whereinthe PET copolymer is present in the polyester composition in an amountfrom about 99.9% to about 97% by weight of the polyester composition andthe additive is present in the polyester composition in an amount fromabout 0.1% to about 3% by weight of the polyester composition.
 9. Apolyester composition as in claim 5 wherein the additive is selectedfrom the group comprising 1,2-dihydroxy naphthalene, 1,3-dihydroxynaphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and2,6-dihydroxy naphthalene.
 10. A polyester composition as in claim 1wherein the polyester has a free volume and at least a portion of theadditive is unreacted with the polyester and disposed in the free volumeof the polyester.
 11. A polyester composition as in claim 1 wherein thepolyester comprises a poly(ethylene terephthalate) based copolymer (PETcopolymer) and, based on 100 mole % diacid component and 100 mole % diolcomponent, the PET copolymer has less than 20% diacid componentmodification and less than 10% diol component modification, and at leasta portion of the additive is reacted with the PET copolymer such thatthe diol component comprises 0.1 to about 5 mole % of the additive. 12.Method for enhancing gas barrier or gas scavenging capability of apolyester composition comprising blending a polyester and an organic gasbarrier enhancing additive having the chemical formula OH-AR—OH, whereinAR is substituted or unsubstituted naphthalene.
 13. Method as in claim12 wherein the polyester is present in the polyester composition in anamount from about 99.9% to about 90% by weight of the polyestercomposition and the additive is present in the polyester composition inan amount from about 0.1% to about 10% by weight of the polyestercomposition.
 14. Method as in claim 12 wherein the additive is selectedfrom the group comprising 1,2-dihydroxy naphthalene, 1,3-dihydroxynaphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and2,6-dihydroxy naphthalene.
 15. Method as in claim 12 wherein theadditive is 1,3-dihydroxy naphthalene.
 16. Method as in claim 12 whereinthe polyester comprises a poly(ethylene terephthalate) based copolymer(PET copolymer) having less than 20% diacid component modificationand/or less than 10% diol component modification, based on 100 mole %diacid component and 100 mole % diol component.
 17. Method as in claim16 wherein the PET copolymer is present in the polyester composition inan amount from about 99.9% to about 90% by weight of the polyestercomposition and the additive is present in the polyester composition inan amount from about 0.1% to about 10% by weight of the polyestercomposition.
 18. Method as in claim 16 wherein the PET copolymer ispresent in the polyester composition in an amount from about 99.9% toabout 95% by weight of the polyester composition and the additive ispresent in the polyester composition in an amount from about 0.1% toabout 5% by weight of the polyester composition.
 19. Method as in claim16 wherein the PET copolymer is present in the polyester composition inan amount from about 99.9% to about 97% by weight of the polyestercomposition and the additive is present in the polyester composition inan amount from about 0.1% to about 3% by weight of the polyestercomposition.
 20. Method as in claim 16 wherein the additive is selectedfrom the group comprising 1,2-dihydroxy naphthalene, 1,3-dihydroxynaphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and2,6-dihydroxy naphthalene.
 21. Method as in claim 12 wherein thepolyester has a free volume and at least a portion of the additive isunreacted with the polyester and disposed in the free volume of thepolyester.
 22. Method as in claim 12 wherein the polyester comprises apoly(ethylene terephthalate) based copolymer (PET copolymer) and, basedon 100 mole % diacid component and 100 mole % diol component, the PETcopolymer has less than 20% diacid component modification and less than10% diol component modification, and at least a portion of the additiveis reacted with the PET copolymer such that the diol component comprises0.1 to about 5 mole % of the additive.
 23. A container comprising apolyester composition comprising: a polyester; and an organic gasbarrier enhancing additive having the chemical formula OH-AR—OH, whereinAR is substituted or unsubstituted naphthalene.
 24. A container as inclaim 23 wherein the container is a stretch blow molded containercomprising a base, an open ended mouth, and a body extending from thebase to the open ended mouth.
 25. A container as in claim 23 wherein thepolyester is present in the polyester composition in an amount fromabout 99.9% to about 90% by weight of the polyester composition and theadditive is present in the polyester composition in an amount from about0.1% to about 10% by weight of the polyester composition.
 26. Acontainer as in claim 23 wherein the additive is selected from the groupcomprising 1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene,1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxynaphthalene.
 27. A container as in claim 23 wherein the polyestercomprises a poly(ethylene terephthalate) based copolymer (PET copolymer)having less than 20% diacid component modification and/or less than 10%diol component modification, based on 100 mole % diacid component and100 mole % diol component.
 28. A container as in claim 27 wherein thePET copolymer is present in the polyester composition in an amount fromabout 99.9% to about 90% by weight of the polyester composition and theadditive is present in the polyester composition in an amount from about0.1% to about 10% by weight of the polyester composition.
 29. Acontainer as in claim 27 wherein the PET copolymer is present in thepolyester composition in an amount from about 99.9% to about 95% byweight of the polyester composition and the additive is present in thepolyester composition in an amount from about 0.1% to about 5% by weightof the polyester composition.
 30. A container as in claim 27 wherein thePET copolymer is present in the polyester composition in an amount fromabout 99.9% to about 97% by weight of the polyester composition and theadditive is present in the polyester composition in an amount from about0.1% to about 3% by weight of the polyester composition.
 31. A containeras in claim 27 wherein the additive is selected from the groupcomprising 1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene,1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxynaphthalene.
 32. A container as in claim 23 wherein the polyester has afree volume and at least a portion of the additive is unreacted with thepolyester and disposed in the free volume of the polyester.
 33. Acontainer as in claim 23 wherein the polyester comprises a poly(ethyleneterephthalate) based copolymer (PET copolymer) and, based on 100 mole %diacid component and 100 mole % diol component, the PET copolymer hasless than 20% diacid component modification and less than 10% diolcomponent modification, and at least a portion of the additive isreacted with the PET copolymer such that the diol component comprises0.1 to about 5 mole % of the additive.